This proposal is directed to investigate the role in KS pathogenesis and KSHV biology of the viral G protein coupled receptor encoded by ORF74 of KSHV (vGPCR). vGPCR appear to be a critical gene in KSHV pathobiology because it can trigger important signaling cascades and induce cellular responses that recapitulate the KS-phenotype in vitro and in vivo. These include activation of VEGF mediated angiogenicity and tumorigenesis. The tools and knowledge generated by the present application in addition to recent advances in the KSHV field provide the necessary armamentarium to undertake a definitive study in vGPCR pathobiology and assess its validity as therapeutic target. Our working hypothesis is that vGPCR expression during lytic replication has the capacity to regulate and host viral gene expression leading to increased endothelial cell survival during and paracrine angiogenic stimulation. That these activities that are directed to enhance viral replication and infection are pre-neoplastic and pro-angiogenic in EC, and thus vGPCR expression in EC can promote KS-cell and vessel growth and also lead to oncogenic transformation. To study the functional role of vGPCR in KSHV infection and pathogenesis we will modulate vGPCR expression during KSHV infection by activation with the chemokine Gro-a and by vGPCR-null mutations. To study the role of KSHV in infection and replication we will 1-Determine at the cellular and molecular level how vGPCR-modulation affects the ability of KSHV to infect and replicate in 293 and endothelial cells. 2- Study how vGPCR expression affects cell survival, survival signaling and KSHV gene transcription during KSHV infection. To determine the role of vGPCR in KSHV mediated Kaposi's sarcoma pathogenesis we will study 1- The contribution of vGPCR to paracrine activation of angiogenesis by KSHV infection using "in vitro" and "in vivo" models. 2- The contribution of vGPCR to the recapitulation of KS-like phenotypes in KSHV infected endothelial cells. 3- The participation of vGPCR in primary endothelial cell immortalization, transformation and angiogenic activation. In addition to test the validity of vGPCR as target for AIDS-KS therapy, this research will provide models that identify vGPCR pathogenic responses in the context of KSHV infection and identify approaches targeted to vGPCR function that are able to block KSHV pathogenesis.